IG window units are known in the art. For example, see U.S. Pat. Nos. 6,632,491, 6,014,872; 5,800,933; 5,784,853; 5,557,462; 5,514,476; 5,308,662; 5,306,547; and 5,156,894, all of which are hereby incorporated herein by reference. An IG window unit typically includes at least first and second substrates spaced apart from one another by at least one spacer and/or seal. The gap or space between the spaced apart substrates may or may not be filled with a gas (e.g., argon) and/or evacuated to a pressure less than atmospheric pressure in different instances. Solar control coatings, such as low-E coatings, are sometimes used in connection with IG window units in order to block IR rays from reaching the interior of a building on which the IG window unit is located.
Sputter deposited thin film solar control (e.g., low-E) coatings on glass are known in the art. For example, see U.S. Pat. Nos. 8,173,263, 8,142,622, 8,124,237, 8,101,278, 8,017,243, 7,998,320, 7,964,284, 7,897,260, 7,879,448, 7,858,191, 7,267,879, 6,576,349, 7,217,461, 7,153,579, 5,800,933, 5,837,108, 5,557,462, 6,014,872, 5,514,476, 5,935,702, 4,965,121, 5,563,734, 6,030,671, 4,898,790, 5,902,505, 3,682,528, all of which are hereby incorporated herein by reference. Sputter deposition of low-E coatings at approximately room temperature, not using an intentionally heated substrate, is advantageous due to the lower cost of non-heated vacuum coaters, high deposition rate, energy saving during deposition, and lower maintenance.
A sputter-deposited low-E coating usually includes a number of layers, including a silver layer that is deposited directly on a contact/seed layer of a material such as zinc oxide or zinc stannate (ZnSnOx). The silver has transmission in the visible range at appropriate thicknesses and reflection in the IR range of the spectrum. Deposition conditions of the contact/seed layer and layer(s) over the silver determine optical and electrical properties of the silver such as solar heat gain coefficient, emissivity, sheet resistance, and visible transmission. The quality of room temperature sputter-deposited thin silver layers is poor, and heat treatment is often requires to improve the optical and electrical properties of the silver to acceptable levels. Such heat treatment (HT) is typically done in a convection oven, e.g., performed in combination with glass tempering for temperable products. However, there are also non-temperable and non-tempered products which do not have the advantage of having had the silver subjected to the HT during the tempering process.
It would be desirable to be able to improve the quality of sputter-deposited silver layers, e.g., in the context of low-E coatings, without having to subject the coated article including the coating to a thermal tempering process. Attempts to improve the quality of the room temperature sputter-deposited silver in low-E coatings by IR irradiation have proven problematic because much of the IR radiation if exposed from the coating side of the glass gets reflected by the silver, or if exposed from the glass side of the coated article gets first absorbed by the glass before reaching the coating and can damage the glass substrate before the temperature elevates to levels sufficient for improving the silver quality. It has been found, in accordance with certain example embodiments of this invention, that UV exposure is highly advantageous with respect to improving the quality of sputter-deposited silver layer(s), e.g., in the context of low-E coatings. For example, the coated article (e.g., glass substrate with a low-e coating thereon) can be exposed from the coating side so that the UV is absorbed by part(s) of the coating without damaging the glass substrate, and much of the UV is able to pass through the silver layer(s) without being reflected before it can perform the desired heating by heating up other layer(s) which are capable of transferring heat to the silver in order to improve its optical and electrical and properties. Thus, in certain example embodiments of this invention, UV exposure of a low-E coating can be used to efficiently improve optical and/or electrical properties of silver based layer(s), and thus also improve such properties of the overall coating, such as one or more of solar heat gain coefficient, emissivity, sheet resistance, and visible transmission.